1. Field of the Invention
The present invention relates to a device for driving and detecting an oscillator for use in, for example, an angle sensor, more specifically, to a device for driving and detecting an oscillator so as to stably drive and detect the oscillator by removing noise produced in the sensor.
2. Description of the Prior Art
FIG. 7 is a block diagram showing a conventional device for driving and detecting an oscillator as well as the construction of part of a angular speed sensor.
The angular speed sensor shown in FIG. 7 has an oscillator 1 as sensing means, a drive control portion for oscillating and driving the oscillator 1 at a predetermined driving frequency, a detection control portion for detecting an angular speed outputted from the oscillator 1, and a correction portion for making sensitivity adjustment and offset adjustment for the oscillator 1 varied by temperature.
The oscillator 1 is, for example, a piezoelectric type oscillator or a capacitance type oscillator, and has a plurality of oscillation legs (for example, three legs) formed in a branched manner at one of the ends of the oscillator 1 extending longitudinally. A pair of input electrodes extending longitudinally are formed in one of the faces of each of the oscillation legs, and a pair of output electrodes are likewise formed in the other face (not shown). In the oscillator 1, when a sine-wave driving signal is given from a drive means 6 to the input electrodes of each of the oscillation legs, the oscillation legs are oscillated and driven in the direction in which the oscillation legs are aligned. In this state, when the oscillator 1 is placed on the longitudinal axis, Coriolis force produced corresponding to the magnitude of rotation allows the oscillator 1 to be deflected and deformed in the direction orthogonal to the oscillation direction. In this deformation, a pair of the output electrodes defined in the other face formed in the oscillator 1 output output signals of different phases corresponding to the magnitude of the Coriolis force.
The drive control portion is constructed of a PLL (phase-locked loop) consisting of binarization means 2, a phase detection portion 3, a VCO (voltage control oscillator) 4, a frequency divider 5, and the drive means 6. When a driving signal SD is outputted from the drive means 6 and inputted to the oscillator 1, output signals S1, S2 are outputted from the oscillator 1.
The phase detection portion is constructed of the phase difference detection portion 3 and a low-pass filter 7, and outputs an angular speed output Sp corresponding to the magnitude of the Coriolis force based on the phase difference between the both output signals S1, S2 outputted from the oscillator 1. An oscillating signal generated by the VCO 4 is frequency-divided by the frequency divider 5. The resulting signal is then sent out, as a reference signal Dref, to a sequence controller 9 at the correction side.
The correction portion is constructed of correction means 8, the sequence controller 9, an E2PROM 10, an E2PROM interface 11, a RAM (Random Access Memory) 12, and a temperature sensor 13. The correction means 8 has a correction circuit 8A consisting of a sensitivity correction circuit, an offset correction circuit, and a temperature coefficient correction circuit, and amplification means 8B.
The E2PROM 10 holds various initial data pieces for sensitivity adjustment, offset adjustment, and temperature coefficient of the oscillator 1 at a certain temperature (for example, 20xc2x0 C.). In the correction means 8, the respective initial data pieces held in the E2PROM at predetermined time intervals based on the reference signal Dref given from the frequency divider 5 under control of the sequence controller 9 are sent out through the E2PROM interface 11 to the RAM 12. In other words, the contents of the RAM 12 is always overwritten with the initial data pieces having the same contents. When the contents of the initial data pieces recorded into the RAM 12 are changed even temporarily due to the influence of noise, the original initial data pieces can be returned immediately.
The correction circuit 8A is provided in its interior with D/A conversion means, not shown, for converting each piece of the initial data pieces to an analog signal. The correction circuit 8A is also fed temperature data piece detected by the temperature sensor 13. The correction circuit 8A selects a sensitivity correction value, a temperature correction value, and a temperature coefficient based on the temperature data piece detected by the temperature sensor 13, and determines a proper amount of offset. The amount of offset is given to the amplification means 8B so as to correct the angular speed output Sp outputted from the phase detection portion 3. The corrected output, whose high-frequency component is removed by the low-pass filter, is outputted as a final angular speed output Spxe2x80x2.
The conventional device for driving and detecting an oscillator has the following problems.
In the abovementioned construction, for example, the binarization process in the binarization means 2 is performed at a frequency in which the frequency of the oscillating signal of the VCO 4 is frequency-divided bisectionally five times (1/32 times), and writing from the E2PROM 10 to the RAM 12 is performed at a frequency in which the oscillating signal of the VCO 4 is frequency-divided bisectionally (1/2 times). In this case, the timing in which the output signals S1, S2 of the oscillator 1 are binarized by the binarization means 2, and the timing in which the respective initial data pieces in the E2PROM are written into the RAM 12 in the correction portion, correspond with each other once in every 16 times.
When the respective initial data pieces of the E2PROM 10 is written into the RAM 12, noise tends to occur.
When the timings of both correspond with each other, a whisker noise is superimposed on the input signal of the binarization means 2 (an output signal of the oscillator 1 and/or a threshold value for binarizing the output signal). When the timings of both do not correspond with each other, the whisker noise is not superimposed on the input signal at all.
As described above, when the whisker noise is superimposed on the input signal, binary signals D1, D2 are varied, and the phase difference between the both signals is also varied due to the variation. For this reason, the control voltage of the VCO 4 is fluctuated, so that the oscillating signal of the VCO 4 is also varied. This fact causes the signals of the entire driving and detecting device to be varied. Since this state is just similar to the state the driving signal SD for driving the oscillator 1 is FM-modulated, the oscillator 1 cannot be driven stably.
The binary signals D1, D2 themselves are varied at a relatively high frequency, but the angular speed output Sp outputted from the phase difference detection portion 3 is varied at a low frequency. It is thus difficult to remove the variation in the low-pass filter 7 at the later stage. The angular speed output Spxe2x80x2 with high accuracy cannot be detected.
The present invention solves the foregoing conventional problems, and an object of the present invention is to provide a device for driving and detecting an oscillator so as to be driven stably without being affected by noise.
Another object of the present invention is to provide a device for driving and detecting an oscillator so as to detect an angular speed with high accuracy without being affected by noise.
According to the present invention, a device for driving and detecting an oscillator comprises an oscillator for outputting output signals of different phases when an angular speed is given, a drive control portion for driving the oscillator, and a detection control portion for detecting the angular speed output based on the output signals of the oscillator, the detection control portion having binarization means for converting the both output signals to binary signals corresponding to the amplitude polarity, a phase detection portion for detecting the angular speed output based on the phase difference component between the both binary signals, a correction portion for performing a correction process for the output of the phase detection portion corresponding to the characteristic of the oscillator, and data holding means provided in the correction portion for holding the contents of memory overwritten with data pieces stored in a data store portion, wherein
the operation of the data holding means is controlled so as to temporarily rest the overwriting of the memory for a fixed period including the time for switching the amplitude polarities in the binarization means.
In the present invention, the operation of a noise producing source (the data holding means) is stopped temporarily for a fixed period before and after, and including the timing for switching in the binarization means. Thus, the binary signals as the output of the binarization means can be prevented from being varied.
In the present invention, preferably, the device for driving and detecting an oscillator further comprises a controller for controlling the overwriting process for the memory in the data holding means, wherein supply of a timing signal (Sc) as the operational reference of the controller is stopped for the fixed period, so as to temporarily rest the overwriting of the memory.
The drive control portion has a voltage control oscillator for controlling the oscillating frequency based on the output signal of the oscillator, and frequency dividing means for frequency-dividing a signal outputted from the voltage control oscillator so as to generate a driving signal of the oscillator, wherein the outputs of flip-flops constructing the frequency dividing means are combined to generate the timing signal (Sc) having the rest period.
In the abovementioned construction, the signal inputted to the frequency dividing means is combined with any one of the output signals of a plurality of the flip-flops constructing the frequency dividing means. Thus, the time width of the rest period can be set optionally. Since the rest period can afford time previously, the construction cannot be affected even when the time for producing noise is somewhat extended.
In the present invention, the oscillator can be a piezoelectric type oscillator or a capacitance type oscillator.